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When I want to create impeller surfaces, MixSim issues the error message...: Error: get-thread: invalid thread id (integer) or name (symbol)(This may also appear in other occasions, and is still very likely to have still the same root cause and resolution..:)Most probably, the following has happened:- You created or loaded a MixSim model.- You created a grid for this (applies also if you interrupted and aborted the mesh generation after just a few Gambit commands had actually been executed)- You loaded an existing (FLUENT) case file.- You tried to do some action in which MixSim needs to tell its internal FLUENT component a zone name. During the above mentioned grid generation run (even it was only partial), MixSim created new zone names which don't fit together with those in the case file that you loaded. In most cases, MixSim will give you a warning when you load a case file that is likely to not fit together with the model in memory. But it fails to do so if you attempt a grid generation between loading an existing MixSim model file and loading the FLUENT case file that should fit together with it. Resolution: Whenever you intend to use an existing case file in MixSim, make sure you start a new MixSim session, load the right model file, and then immediately load the FLUENT case file. When you follow this procedure, MixSim should be able to warn you if there's any danger that the FLUENT case may not fit together with the MixSim model in memory.